Three characteristics of pharmaceutical formulations are: physical, such as size, hardness, friability, disintegration and dissolution; chemical, such as drug content and stability and sensory, such as appearance, odor and taste. All of the three characteristics are equally important with respect to patient acceptance, preference and compliance. For example, an unpleasant odor in a formulation reduces patient acceptance, preference and compliance. Film coating is a well known art. Pharmaceutical solid dosage forms such as tablets, granules, pellets etc are film coated to protect these solid dosage forms from oxidation due to atmospheric oxygen permeation, moisture, heat, light, etc as well as to mask the odor of the pharmaceutical preparations.
Many nutraceutical and some pharmaceutical preparations are associated with unpleasant odor and taste and are susceptible to moisture or oxygen induced changes. Examples of such nutraceutical preparations are valerian root extract, garlic and many multivitamin preparations etc. Conventional approaches for masking odors of pharmaceuticals utilize sugar coating technology. Sugar coating requires non perforated coating pan, long processing times and experienced personnel to obtain products of acceptable quality, i.e., odor masking. This coating process produces tablets which are nearly double the weight of the starting core. Due to the problems associated with sugar coating technology, film coating has gained importance. There are various other methods to mask odors. One way is to add flavors to the formulation to change the taste. The goal is to make the formulation more acceptable and to increase the consumer compliance with the dosage regimen.
Protection of dosage form from environmental moisture is important when the drug is adversely affected by its presence. Common approach used to limit the degradation is to package the moisture sensitive dosage forms, such as tablets, capsules etc using specialized packaging. In places where climate is very humid the special packaging does not provide the complete moisture protection. Another way to reduce the need for special packaging is to coat the solid dosage forms with materials which reduce the moisture uptake. Moreover, these coatings should not affect the disintegration times. Examples of moisture sensitive drugs are ranitidine, temazepam, most vitamins and numerous herbals. Examples of moisture induced changes can range from degradation of drug by hydrolysis or changes in the appearance of the dosage form on storage to changes in the disintegration and dissolution times of the dosage form. Moisture barrier coatings are thus applied to augment or eliminate the need for special packaging. It protects the dosage form from degradation.
In order to achieve a moisture barrier coating, usually hydrophobic or lipophilic substances are combined with water soluble or water insoluble film forming polymer and pigments. The hydrophobic or lipophilic substances may be a polymer where the polymers generally employed for this purpose are shellac, cellulose acetate phthalate (CAP), ethylcellulose (EC) and the like. However, when coating with these polymers, use of organic solvent is typically required which also necessitates the added expense for air conditioning equipment, anti-explosion provisions, and the like to safely handle such materials. Another disadvantage of the use of these polymers is the prolonged disintegration of the dosage form in the body when ingested due to the reduced aqueous solubility of coatings made from polymers which rely upon organic solvents to process these materials into coatings.
U.S. Pat. Nos. 6,495,163 and 5,885,617 each disclose a moisture barrier film coating composition comprising polyvinyl alcohol (PVA), soya lecithin, flow aid, colorant and suspending agent. These coatings use medium viscosity grades of PVA which dissolve readily in cold water and still maintain moisture barrier properties. However, it is well known that PVA is extremely tacky and application of coatings based on PVA requires slower spray rates, higher atomization pressures and higher bed temperatures during a film coating process. This is disadvantageous to the dosage manufacturer as it doubles the coating time for a solid dosage form and thus increases the overall cost of the process used to produce coated solid dosage forms. Moreover, coatings utilizing PVA do not mask unpleasant odors produced by active ingredients.
U.S. Pat. No. 4,341,653 discloses a protective coating composition comprising a metal salt of higher fatty acid, a higher fatty acid and a wax in an aqueous solution of a water soluble film base and a surface active agent. However, this coating was produced as an emulsion which has an additional homogenization step. Also, the coatings taught in this patent are designed to delay the dissolution time to mask the taste of the active in addition to providing moisture barrier.
JP2006188490A teaches a film coating composition with improved adhesiveness, excellent coating properties which masks the smell and provides oxygen barrier. This coating comprises a polyvinylalcohol and talc and does not provide barrier to moisture.
U.S. Pat. No. 5,077,053 teaches use of Zein as a moisture barrier for sugarless edible compositions. In this composition, a two layered coating is required. The first layer being a layer of Zein and a second lay being a sugarless layer.
U.S. Pat. No. 6,667,059B2 teaches a multilayer odor barrier coating, particularly for use in valerian root tablets. In this composition, the first two layers are composed of hydroxyalkyl cellulose followed by third layer of methacrylate. Besides being time consuming to produce, this coating is not acceptable for nutraceutical uses as methacrylates are not acceptable for food use.
The disadvantages associated with above mentioned coating approaches are that the coatings are either difficult or time consuming to apply, which makes the process less cost effective, or they increase the disintegration time of the coated solid dosage form upon ingestion.
In summary, a need exists for a multifunctional barrier coating which provides moisture, odor as well as taste barrier for various nutraceutical and pharmaceutical solid preparations. There is also a need for a multifunctional barrier coating that is easy to produce from a powder and easy to apply to the solid dosage form.